Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Wilmington Ohio
413 PM EDT Wednesday Apr 1 2015
high pressure and dry airmass will move off to the east tonight. A
frontal zone will develop on Thursday and remain in the area through
Friday. Several waves of low pressure traveling along the front will
provide multiple rounds of rainfall. High pressure and dry air
will move back in for Saturday.
Near term /until 6 am Thursday morning/...
middle level ridge to build east into Great Lakes/Ohio Valley with surface
high pressure sliding off to the East Coast by this evening. A
return southerly low level flow to develop on the backside of this
retreating surface high pressure. Expect mainly clear skies this evening
with an increase in clouds...thickest over the west late tonight.
Southerly flow and the increase in clouds late will keep
temperatures on the mild side tonight. Low temperatures to range
from the lower 40s northeast to the upper 40s southwest.
Short term /6 am Thursday morning through Friday night/...
slow moving cold front to approach from the west Thursday and move
into Ohio Thursday night. Northern stream energy to pass north of the
Great Lakes with southern stream trough holding back over the Southern Plains.
This keeps iln/S forecast area in a moist southwesterly flow. 50-60 knots low level jet
with enhanced low level convergence developing Thursday evening.
Favorable moisture transport for a prolonged period. Precipitable
water values increase to close to around 250 percent of normal or 2
to 3 Standard deviations above normal Thursday night. Will continue
likely probability of precipitation across the west Thursday afternoon and categorical Thursday
night. Marginal instability develops Thursday afternoon/Thursday evening. With the front
still to our west...storms will have to be cold pool driven. Expect
marginal instability with boundary layer convective available potential energy less than 1000 j/kg.
Although wind flow will be favorable the instability will be limiting
factor and expect ongoing storms to weaken as they track NE away
from more favorable instability axis. Will continue to mention this
marginal potential in the severe weather potential statement product.
In strong warm air advection pattern temperatures to be 20-25 degrees above normal
Thursday with highs from the upper 60s northwest to the Lower/Middle 70s
Embedded middle level short wave in the southwesterly flow will induce a surface
wave on the frontal boundary. This wave to ripple NE through the Ohio
Valley late Thursday night/early Friday. This wave will provide an
enhanced chance of precipitation with favorable low level forcing. Lows
Thursday night from the upper 40s northwest to the upper 50s
southeast. With surface wave/front bisecting the area...there will be
a large gradient in temperatures on Friday. Fridays highs are expected
to range from the middle 50s northwest to upper 60s southeast.
Flows merge with mean trough over the Great Lakes by Sat morning.
Numerical model solutions differ some on placement but all have a final
surface wave passing through the Ohio Valley Friday night.
Due to the prolonged period of precipitation and the moist
environment the potential for heavy rain will exist. Numerical model
solutions suggest 1 to 3+ inches of rain but differ on amounts and
placement. At this time will continue to highlight heavy rain and
the potential for flooding in the severe weather potential statement product.
In cold air advection on backside of departing low pressure temperatures drop to
lows from near 30 northwest to the upper 30s southeast by Saturday morning.
A brief period of snow is possible prior to ending late Friday
night but deep moisture and best lift exits quickly so do not
expect significant snow. At this time only have one to two tenths
in the N-NE.
Long term /Saturday through Wednesday/...
precipitation will be exiting the eastern County Warning Area early Saturday
morning as surface high pressure and much drier air builds in from
the west. Despite mostly sunny skies...a broad upper trough and
850 temperatures around minus 5 c will make for a chilly day with highs
ranging from the middle 40s north to lower 50s south. Lows Saturday
night will again drop into the 30s across the area...before warm air advection
kicks in on Sunday allowing temperatures to return back to near normal. A
frontal boundary stalled north of Ohio will keep chances for
showers north of the County Warning Area on Sunday. Cloud cover will consequently
be more prevalent across the northern half of the County Warning Area.
Deterministic models and ensemble guidance then diverge
significantly for the remainder of the extended period. Generally
used an equal blend of wpc guidance...GFS and European model (ecmwf) for Monday
through Wednesday. GFS is quicker than European model (ecmwf) to bring the next
system into the Great Lakes region late Monday into Tuesday. The iln
County Warning Area will be in the warm sector both days with persistent warm air advection
allowing temperatures to warm into the upper 50s to middle 60s on Monday and
into the middle 60s to near 70 on Tuesday. Isentropic lift will provide
a chance of showers during the day on Monday. A developing low level jet
Monday night will then transport ample Gulf moisture into the Ohio
Valley with precipitable waters around 1 to 1.5 inches (over 200 percent of
normal) on Tuesday. Precipitation chances will be highest Monday night into
Tuesday and have included thunder in the grids on Tuesday as
favorable instability develops thanks to the increasing warmth and
low level moisture.
Chances for showers and isolated thunder will continue into
Wednesday as a cold front drops southeast across the area. Low
confidence in timing of frontal passage however as GFS is quick to push it
through Tuesday night and European model (ecmwf) does not push it through until later
Aviation /20z Wednesday through Monday/...
VFR will continue through the early part of the forecast as high
pressure and a dry airmass recede east. Skies will be mainly
clear to start...before cirrus clouds begin to overspread taf
sites tonight from the southwest ahead of a developing frontal
As the front approaches on Thursday...showers will be possible in
the vicinity of taf sites starting around 12z. Expect conditions
to remain VFR as the showers develop Thursday morning.
For the 30 hour taf at cvg...showers will become prevalent after
18z Thursday. Thunderstorms may occur in the vicinity...and MVFR
conditions are anticipated as low level moisture increases as per
latest model projections.
Winds will increase out of the south by the end of the forecast
period...with gusts over 20 knots expected.
Outlook...MVFR ceilings and visibilities are possible Thursday
night into Friday night.